In this paper

a concept of voltage stability margin with partial voltage stability L is the base and an improved particle swarm optimization algorithm are proposed.Firstly

the weak node of the system voltage is identified by the use of the voltage stability margin of the load node and this is taken as reactive power compensation point.The margin is free from load growth mode and has defined upper and lower bounds.Then

with the minimum active power network loss as objective function

the reactive power optimization mathematical model of the power system is set up

and the improved particle swarm algorithm is proposed further.Introduction of"fly back"strategy and quadratic interpolation in the algorithm improves partial search ability and convergence speed.With the proposed method

the reactive compensation of the system is balanced and the reactive power source is allocated reasonably.Finally

the reactive power optimization of the IEEE 30 node system is made and the effectiveness of the proposed method is shown by the Matlab simulation result.